238 TATE: LAKE COUNTRY ROCKS. 
by the marked absence of boulders both from the north, east, and 
south—Skiddaw, Carrock Fell, and Borrowdale. 
Of the numerous rocks possessing distinctive characters by which 
they may be identified when occurring as boulders, some call for 
special notice. The well-known biotite granite of Wasdale Crag, 
near Shap Wells, has pink tabular crystals of orthoclase an inch or 
so long, and matrix with nests of black mica. The very coarse 
granite quarried at Waberthwaite and higher up Eskdale, of which 
there are two varieties, grey and red, is also exposed at the head of 
Wastwater and at the base of Scafell. Skiddaw granite, having 
a friable white matrix, with robust crystals of white orthoclase, is 
exposed near the foot of Brandy Gill, and a larger mass, coarser 
grained, higher up the Caldew. It is easier of access in Sinen Gill 
by ascending the left bank of Glenderaterra, where boulders will 
be seen in its bed near to the copper-mine. Two bosses of quartz- 
felsite flank the lovely Vale of St. John. From the chapel of St. John 
past Low Rigg to a quarry near Hollin Root it is red in many 
places; but it may be more conveniently studied at Threlkeld, where 
it is extensively quarried. It is nearly pure white, inconspicuous 
crystals of orthoclase, quartz, and yellow-green plagioclase embedded 
in a felsitic matrix are its components. Long lath-like crystals of 
biotite appear locally. The beautiful quartz-felsite of the Armboth 
and Helvellyn Dyke, with its bright pink oblong crystals in a red 
felsitic matrix, is exposed in Armboth beck, a feeder of Thirlmere 
Lake, a little above Armboth House; and again half a mile east af 
this near the ordnance cairn ; but boulders are profusely scattered in 
the Vale of St. John, and may be collected off the wall tops on 
approaching Keswick. They are also abundant in the embankment 
of the new road skirting Thirlmere. 
A visit to Carrock Fell, one of the three chief volcanic foci of the 
Lake Country, will amply repay the petrologist. Its structure has — 
been variously interpreted, nor can it be said even yet to have been 
fully worked out. If we follow the beaten track from Mosedale to 
the Fell summit, after climbing over unaltered Skiddaw slates dipping 
sharply into the hill, we come upon what look like bedded layers of 
a fine-grained ferro-magnesian mineral; a little higher the basic 
plates enlarge into distinct crystals of diallage, with which white 
telspar is blended until the rock gradually assumes the appearance of 
a coarse gabbro. More rarely, a delicate rose-tinted felspar replaces 
the white plagioclase. In and about the sheep-cote the structural 
peculiarities of the Carrock Fell gabbro reach a maximum that in 
many hand specimens simulate a coarse pegmatite or graphic granite: 
the presence of quartz along with white felspar, and the sparse basic 
Naturalist, - 
